1. Field of the Invention
The present invention relates to the conversion of heavy hydrocarbon stocks, particularly those containing sulfur, nitrogen and metal contaminants to provide good yields of motor gasolines, jet fuel (kerosene), diesel fuel and distillate fuels. More particularly the invention relates to a hydrocracking conversion process wherein a heavy feed stock is simultaneously cracked to a lighter boiling product and hydrogenated to prevent formation of undesirable unsaturated compounds. More particularly the invention relates to a process wherein the hydrocracking and separation of the lighter products from the heavier uncracked material occurs simultaneously in a distillation column reactor.
2. Related Information
The operating conditions for the hydroconversion disclosed in U.S. Pat. No. 5,100,855 for heavy hydrocarbon streams, such as petroleum hydrocarbon residue and the like, comprise a hydrogen partial pressure of about 1000 psia to about 3000 psia and above, an average catalyst bed temperature of about 700.degree. F. to about 850.degree. F. and an LHSV of 0.1 to 5 hr.sup.-1 ; for hydrocarbon distillates a hydrogen partial pressure of about 200 psia to about 3000 psia, an average catalyst bed temperature of about 600.degree. F. to about 800.degree. F. and an LHSV of 0.4 to 6 hr.sup.-1.
The purpose of hydrocracking is to produce a more valuable distillate product which boils in the range of about 115-650.degree. F. which can be separated into a gasoline fraction (115-400.degree. F.), a kerosene or jet fuel fraction (350-450), a diesel fraction (400-550) or a light heating oil (500-650). The boiling ranges of the different products overlap as noted.
The advantages of hydrocracking over thermal or fluidized bed catalytic cracking is that a more stable product is made. Kerosene (jet fuel) and diesel are particularly benefited by the reduction in unsaturated compounds. Gasoline boiling range material from a hydrocracker, while low in octane, is particularly suitable as feed to the reforming units because of low sulfur, nitrogen and olefin contaminants.
A conventional hydrocracker is a series of beds in a vertical reactor with the charge being passed downflow in concurrent flow with hydrogen. The reactions taking place are exothermic, resulting in a temperature rise in each bed. Temperature is controlled by the addition of cold hydrogen quench between each bed.
In U.S. Pat. No. 4,194,964, Chen, et al propose a process operated at about 300 psig to 3000 psig and high hydrogen partial pressures for concurrent hydroprocessing and distillation of heavy petroleum stocks. Essentially, Chen et al disclose the use of concurrent distillation and hydroprocessing of the heavy stocks for the standard high pressure treating and hydrocracking. The range of conditions is fairly consistent with the prior art processes. Chen et al specifically disclose hydrocracking at elevated pressures of 750 and 1000 psig with the unexpected result that separation by distillation can be achieved at the higher pressures.
Chen et al call for a column conducting reactions and distillations, but failed to disclose how to achieve such a column while operating an experimental packed column for the reactions, which appear as a single stage flash rather than a true distillation.
A method of carrying out catalytic reactions has been developed wherein the components of the reaction system are concurrently separable by distillation using the catalyst structures as the distillation structures. Such systems are described variously in U.S. Pat. Nos. 4,215,011; 4,232,177; 4,242,530; 4,250,052; 4,302,356 and 4,307,254 commonly assigned herewith. In addition, commonly assigned U.S. Pat. Nos. 4,443,559, 5,057,468, 5,262,012 5,266,546 and 5,348,710 disclose a variety of catalyst structures for this use and are incorporated by reference herein.
While Chen et al have obtained hydrocracking at lower than previous pressures (about 2000 psig has previously been considered necessary for hydrocracking), the present invention provides a process that operates at only a fraction of the pressures used by the general prior art and below the lowest pressure projected by Chen et al.